1. Field of the Invention
The present invention relates, generally, to bipolar plates for direct methanol fuel cells, more particularly, to the structure of a bipolar plate for direct methanol fuel cell which can increase a reaction region between fuels and a catalyst layer as well as easily supply fuels to an electrode for direct methanol fuel cell and improve dispersion of the supplied fuel to enhance the performance of a fuel cell and the shape of a flow path and a direct methanol fuel cell including the same.
2. Description of the Related Art
Recently, as various goods are manufactured in accordance with the rapid development of an information communication technology, a technology related to portable electronic equipment such as cellular phones, laptop computers, personal digital assistants (PDA), digital cameras and camcorders has been remarkably growing.
The development of the technology related to the portable electronic equipment is represented in a high functionalization of portable electronic equipment in order to satisfy the tastes of the consumers requiring for more information.
However, this high functionalization was limited in a continuous use due to a large energy consumption and therefore, a device for supplying with energy became a core technology affecting the capability of electronic products. This technical request became a motive force to encourage researches and developments of a technology related to fuel cells in the developed countries like the USA and Japan.
A fuel cell is a device for directly converting a chemical energy into an electric energy, in which an oxidation reaction of a fuel occurs in an anode and a reduction reaction of oxygen occurs in a cathode. The basic structure of a fuel cell consists of a catalyst carrying anode, a cathode, a membrane/electrode assembly which is manufactured by inserting electrolyte layer between the anode and the cathode and a bipolar plate positioned on both surfaces of the membrane/electrode assembly. In the membrane/electrode assembly, the electrode functions as covering platinum catalyst on a carbon paper or a carbon cloth to directly induce the oxidation and reduction reactions of fuels through a catalyst and an electrolyte membrane functions as delivering hydrogen ions from an anode to a cathode due to a catalyst operation and as a separator keeping fuels from directly being mixed with oxygen.
In addition, the bipolar plate functions as supporting the membrane/electrode assembly, supplying and emitting methanol and oxygen which are supplied as a fuel to a cathode and an anode, respectively, and emitting the water produced in the cathode as well as functions as a collector for inducing the electrons produced in the anode to the cathode.
Currently, a bipolar plate for direct methanol fuel cell is made of a metal like a stainless steel or a graphite block of which corrosion and weight are improved. A flow path mainly has a serpentine type structure. However, the serpentine type structure increases a fluid-flow resistance when fuels are supplied to make it difficult to supply a fluid and disturb an activation reaction of electrodes, therefore the performance of a fuel cell may be degraded. Accordingly, researches and developments of a bipolar plate having the new shape and structure of a flow path are required in order to obtain the improved performance of a cell by improving a fluid-flow resistance.
Meanwhile, as the prior art about a flow path for fuel cell related to the present invention, a bipolar plate having a serpentine type flow path was disclosed in U.S. Pat. No. 4,988,583, U.S. Pat. No. 5,521,018 and U.S. Pat. No. 6,358,642 and Journal of Power Sources 114 (2003) 54, Atul Kumar, R. G. Reddy, etc. However, this bipolar plate based on a flow path with a serpentine type structure cannot avoid an increase of a fluid-flow resistance when fuels are supplied. Therefore, it becomes difficult to easily supply fuels and a phenomenon that the performance of a fuel cell decreases is shown. Accordingly, researches and developments of the structure of a bipolar plate and the shape of a flow path are desperately requested in order to improve the capability of a fuel cell.